Circuit breaker apparatus



Jan. 7, 1969 M. AU PETIT CIRCUIT BREAKER APPARATUS Sheet Filed June 16. 1965 Filed June 16. 1965 Sheet I Jan. 1, 1969 M. AU PETlT CIRCUIT BREAKER APPARATUS Filed June 16, 1965 Sheet United States Patent 3,420,971 CIRCUIT BREAKER APPARATUS Marcel Aupetit Rueil-Malmaison, France, assignor to La Telemecanique Electriqne, Nanterre, Seine, France, a company of France Filed June 16, 1965, Ser. No. 464,287 Claims priority, application France, June 22, 1964, 979,205; May 13, 1965, 16,966 US. Cl. 200144 Int. Cl. H01h 33/00;I-I01h 9/30 Claims ABSTRACT OF THE DISCLOSURE This invention relates to circuit breaking switch devices of the type used for Opening electric power circuits under high loads.

In devices of this class, considerable problems are created by the high-powered arc which is struck across the contact surfaces of the circuit breaker as these surfaces separate during a circuit-breaking action. One widely used method of handling the arc is to propel the arc toward a quenching zone positioned beyond the ends of the contact members of the circuit breaker. The quenching zone may operate on the so-called deion principle, according to which the arc is split up into a plurality of shorter arcs which can be rapidly extinguished.

Whatever the method of arc quenching used, it has generally been found necessary, in high-capacity circuitbreakers of the prior art, to provide some means of compelling the arc to travel in a perscribed direction over the separating contact surfaces and to the ends of the circuitbreaker contact members (in order to be delivered to a deion quenching chamber or the like) while preventing the are from escaping laterally off the sides of the contact surfaces. The means generally provided for this purpose have taken the form of strong magnetic fields and/ or strong air blasts operative to propel the arc in the prescribed direction. The need for such powerful, auxiliary arc-driving means have seriously complicated the construction and maintainance of high-load circuit-breakers and increased their cost.

It is a primary object of this invention to eliminate the requirement for any such auxiliary are driving force means and correspondingly to simplify the construction and construction of high-power circuit-breakers.

Another object is to provide an improved circuitbreaker construction wherein the electromagnetic forces generated by the paths of electric current flow through the device during a circuit breaking action, will inherently be of such character that they will propel the arc in a pre scribed direction, regardless of the particular point at which the arc may be initiated, and without the provision of any auxiliary, extraneous means.

It will be understood that the contact surfaces of a high-power circuit breaker must be of appreciable surface area in order to take up the high currents involved. As these large contact surfaces separate during a circuit breaking action, the arc is struck at a point randomly located over their area, and which will generally vary in Patented Jan. 7, 1969 random fashion from one circuit breaking action to another. As soon as an arc has been initiated, it is subjected to various forces which cause it to move over the contact surfaces.

Among the forces acting on the arc to move it over the surface of the contacts, are electromagnetic forces created by the magnetic field generated by the paths of current flow through the contact members of the circuit breaker, leading to and from the extremities of the arc.

These electromagnetic forces are, of course, necessarily present in any circuit-breaker. To the applicants knowledge however these internal or inherent electromagnetic forces have never been utilized in order to achieve a desired direction of travel of an are over the contact surfaces in a circuit-breaker. In fact, the applicants investigations have shown that in many conventional circuitbreakers these inherent electromagnetic forces are so directed, due to the geometry of the current conduction paths through the circuit-breaker contact members, that they tend to chase the arc sideways and in a direction to cause the arc to escape laterally from the contact member long before it has reached the outer end thereof. It is essentially for this reason that powerful auxiliary forces, magnetic or pneumatic in character, have had to be used. These auxiliary forces were required primarily to overcome the electromagnetic forces that were inherently present during the circuit breaking action and which, in most conventional high-power breakers, are directed in a direction which has promoted the objectionable sideways escape of the arc.

According to a basic concept of this invention, the geometry of the circuit breaker contact members, especially in the parts thereof through which current flows to and from the breaker contact surfaces, is so determined that the electromagnetic forces generated by said current flow and acting upon the arc, will have a resultant in the right direction to drive the are positively towards the prescribed ends of the contact members, thereby eliminating the need for any extraneous means to that end. Another object of the invention is to maximize this electromagnetic force created in the normal operation of a circuit breaker while ensuring that it is directed in the proper direction.

Other objects will appear. Exemplary embodiments of the invention will now be described with reference to the accompanying drawings, wherein:

FIG. 1 is a side view, taken on the line I-I of FIG. 2, showing the contact members of an improved circuitbreaker, at the start of a circuit breaking action.

FIG. 2 is a front view on line IIII of FIG. 1, showing one of the contact members.

FIG. 2A is a cross sectional view on line IIAIIA of FIG. 1.

FIG. 3 is a view taken on line IIIIII of FIG. 4, showing a complete circuit-breaker unit including arc quenching means, embodying a pair of circuit breaker contact members constructed in accordance with the invention.

FIG. 4 is a view on line IVIV of FIG. 3.

FIG. 5 is a front view of a modified contact member of a circuit-breaker according to the invention.

FIGS. 6 and 7 are views taken on line VIVI and VII-VII respectively, of FIG. 5.

The circuit breaker contact assembly shown in FIGS. 1, 2 and 2A incdludes a stationary contact member A and a movable contact member B, similarly constructed. Each contact member A or B is in the general form of a channel-shaped arm (see FIG. 2A) preferably made of copper, which has a median slot 6 formed longitudinally over a major part of its length from its upper or outer end 12, thereby dividing contact member into two similar halfarms 3. At its lower end the half-arms 3 include a transverse base member 1 with a hole therein for an attaching bolt 2 serving to secure the contact member to a suitable support, stationary or movable as the case may be. Extending along opposite sides of the base 1 and upwardly therefrom are flange sections 3a which have edges that slant away from the base 1 eg at an angle of about 45 as shown in FIG. 1. These angular initial flange sections 3a then merge with the straight flange sections 3b which constitute the side flanges of the channel-shaped main portion of the half-arms 3. The web of this channel portion is constituted by the two coplanar parts 3c, separated by the afore-mentioned slot 6. A contact segment is carried by each member on its web surface facing the other member, i.e. on the parts 30 thereof, and said segment is also divided into halves by slot 6. Each half segment has a flat rectangular contact face 7, the contact faces 7 of both half segments 5 associated with each contact member being coplanar. The half contact element 5 further includes an outwardly slanting bevel edge surface 8 which connects its flat contact face 7 with the outer side edge of the leg 3b of the related half-arm 3, a lower slanting bevel surface 9 which connects contact face 7 with the surface of leg 30, and a short upper bevel surface 10. This upper bevel 10 is coplanar with the angularly-jutting arc quenching end parts 12 which are constituted by the outer or upper ends of the legs 30.

The contact segments 5 are desirably made of silver, and are brazed to the underlying surfaces of the pole members, which are suitably made from a strong copperchromium alloy.

The inwardly facing edge surfaces of the legs 30 diverge as at 11 (FIG. 2) towards the base 1 below the contact elements 5, so as to join up with the inner edges of the bottom parts 3a of the half-arms 3. These diverging edges 11 define between them a triangular enlargement of the slot 6, which is followed adjacent the base 1 by a constant-width section of said slot as defined between the inwardly facing edge surfaces of the parts 3a. It will be noted especially by reference to FIG. 2 that with the arrangement disclosed the midplane of symmetry of each arm section 3a (and of the corresponding arm sec-' tion 3b generally coplanar therewith), which midplane is a vertical plane normal to the plane of the drawing in FIG. 2, is positioned a greater distance from the midplane of symmetry of the pole member C, which is the vertical plane indicated as I in FIG. 2, than the vertical outer edge 5a of the related contact face 5a is positioned. The significance of this geometric relationship will be presently made clear.

In the operation of the circuit breaker, as the movable contact member B is rotated away from the stationary contact pole member C in the direction indicated by arrow F, so that the contact surface 7 of said movable member moves away from its companion contact surface, an arc is generated across the separating contact surfaces 7 at some point over their area. The point at which the arc is first initiated is random and varies randomly from one circuit-breaking operation to another. In accordance with the known principles of operation of arc-quenching circuit breakers of the deion or equivalent types, it is desired that the arc shall travel towards the outer horns 12 of the contact members thence to be conveyed to quenching means in which it will be broken up into a number of short arcs and quenched, as will be more fully described with reference to FIGS. 3 and 4.

In conventional circuit breakers of this type, powerful are blowing means, pneumatic and/ or magnetic in character, were provided in order to propel the are positively towards the horns 12 of the contact members since in the absence of such means the arc had an inherent tendency to travel toward outer edges (such as 5a) of the contact surfaces 5 and toward the pivotal axis of the pole members, that is in a direction different or indeed opposite from the desired one.

In the circuit breaker herein disclosed, such auxiliary are blowing means can be and are entirely eliminated, because the electromagnetic forces generated in the operation of the device are inherently such as to drive the arc positively in the requisite direction i.e. towards the quenching means, without the aid of any auxiliary expedients. This feature in turn results from the geometrical characteristics of the circuit breaker members constructed as described above. The manner in which this geometry succeeds in creating electromagnetic forces possessing the requisite characteristics will now be explained.

As said above the point at which an arc will initiate on separation of the contact faces is randomly located over the area of said faces, but it is clear that the most unfavorable point at which the arc can be initiated is the lower-outer corner (such as X, FIG. 2) of a contact face, since the are when positioned at such a corner will be most likely to escape off the contact surface instead of travelling the full distance thereover towards the pole tip 12, as is desired. Indeed, with repeated operation of any circuit-breaker it is found that the arc tends more and more to initiate at such a lower-outer corner X.

With an are positioned at point X and extending across the airgap between the contact faces 7 of the circuit breaker shown in FIGS. 1, 2 and 2A, the current path energizing each end of the are from the base 1 of the pertinent half-arm 3 of each contact member of the breaker, extends through said arm along a line whose general configuration is that shown at M. That is, said current path after leaving the base 1 follows an oblique segment in the upwardly-inwardly sloping arm section 3a, said segment being positioned substantially in the mid-plane of symmetry of said arm section as clearly shown in FIG. 2.. It will be noted that in this segment extending through the relatively thin arm portion 3a, the current is obliged to flow through a comparatively constricted conductive section, as indicated at S. This ensures that the direction of current flow in this initial segment of the conductive path is well defined, and that the requisite direction of flow is effectively imparted to the arcenergizing current in this initial segment of its path.

On reaching the L-shaped section of the half-arm 3, provided by the arm portions 3b and So at right angles, the arc energizing current tends to separate into two circuit branches in parallel (electrically speaking). One branch extends through arm portion 3b and can be represented as a bunch of current lines m1, and the other branch follows arm portion 30 and can be represented by the bunch of current lines 1112. Both branches m1 and m2 converge and meet at the point X at which the arc is assumed to be located, and the resultant of the current lines m1 and 1112 constitutes the mean path of current flow designated M.

It will be observed that this mean current flow path M, in its ultimate segment where it joins with the are at X, curves inwards towards the plane of symmetry of the pole member (i.e., towards the slot 6) as seen in projection on the plane of FIG. 2, and also curves inwards towards the plane of symmetry of the pair of pole members (i.e., togadslthe airgap) as seen in projection on the plane of The direction of action of the electromagnetic force set up by an arc-energizing circuit having the geometry just described can best be understood by referring to a classical experiment sometimes known as Amperes experiment. Consider a rigid conductive rod freely supported upon a pair of parallel conductive rails which are energized from corresponding ends. The generated electromagnetic forces are such that the rod will be driven over the rails away from their energized ends. This is expressed by the law which states that any circuit will tend to be deformed in the presence of electromagngetic energy in such a sense as to increase its inductance, so that a loop circuit will be distorted in such a sense as to increase its enclosed area.

Returning to FIGS. 1 and 2, it will be apparent that the arc struck across the surfaces 7 at X is comparable to the above'mentioned movable conductive rod of Ampcres experiment, while the current conduction paths M leading through both pole members to the opposite ends of said arc (as shown in FIG. 1) can be likened to the energizing rails and connections. The are will, consequently, be driven by the resulting electromagnetic force in a direction away from the supply ends of said lines M, and specifically in the direction indicated by arrow D in FIGS. 1 and 2. This direction, as seen in projection on the plane of FIG. 1, is parallel to the contact surfaces 7, and as seen in projection on the plane of FIG. .2 coincides with the direction of the tangent to the corresponding projection of line M, as shown in the drawings.

The electromagnetic forces acting on each infinitesimal element of the are are all contained in the plane normal to the contact face 7 and containing the tangent to the end segment of the means current path M projected on the contact face at point X, i.e., the plane indicated by arrow D in FIG. 2, and owing to the curvature of said segment as defined above, the arc will be positively driven by the resultant force in the requisite upward-inward direction without the provision of any auxiliary arc-propelling means. The are, regardless of its point of inception, will be forcibly propelled upwards toward the quenching pole tip 12 and inward toward the edge wall of slot 7, and on reaching the edge of the slot it will continue due upward along that edge until it reaches the pole tip 12 and is discharged from it toward the conventional arc quenching means, not shown in this embodiment.

It will be noticed from FIG. 1 that the current lines m2, previously referred to, which extend through the rectilinear arm portions 3b of the arms of the respective circuit breaker contact members, define upwardly convex circuit loops having parallel and rather closely spaced rectilinear legs situated in the respective pole members. It can be shown that the intensity of the resulting electromagnetic force acting on the arc in the direction just defined above, integrated over the length of said straight parallel segments of the lines m2, is approximately proportional to the sine of the angle indicated as a in FIG. 1, this angle being the 90 degrees complement of angle [3, one half the angular width of the loop defined by the means current path line M. This force can therefore be increased by increasing the angle 0:, which means increasing the length of the lower part of the arms as far as the lower edge of the contact face 7. An excessive increase in arm length is obviously undesirable in that it would tend to render the pole members excessively flexible. It is noted, however, that in view of the above-indicated sine relationship there would be no point in increasing the angle a and the length of the arms beyond a certain value since the resulting increase in the intensity of the electromagnetic force would be comparatively negligible. Thus, if a=60, sin u=0.86, and a further increase in arm length, no matter how great (whereby a. would approach 90), would only achieve a minor increase in electromagnetic force intensity. In accordance with this invention, a suitable range for the angle a in most cases can be taken as 45 to 70, with 60 being a preferred value. However, angular values outside said range may occasionally be used.

FIGS. 3 and 4 illustrate a complete circuit-breaker unit constructed in accordance with an embodiment of the invention. The unit comprises a frame or casing 20 made of insulating material, having power bus terminals 21 and 22 connected to opposite sides of it. A conductive frame member 23 is mechanically and electrically connected to bus terminal 22 and supports the stationary contact member 24 of the circuit breaker suitably screwed thereto as shown. Also screwed to an outer side of frame member 23 is a bracket 25 which supports one side of a generally conventional arc quenching casing 26 the opposite of which is provided with horizontal pins 41 engageable with complementary cutouts formed in uprights 42 projecting from the corresponding side of the frame 20*.

The quencher device 26 is provided with a plurality of spaced partitions 27 and operates on the well-known deion principle whereby the are delivered thereto over the tips or horns 47 of the pole members is broken up into short arcs between the partitions and which are separately quenched.

The circuit breaker includes the stationary contact member 24 and the movable contact member 29a-29b, which are basically similar in configuration to the pole members described in the first embodiment, except for differences noted later.

Bus terminal connector 21 is connected by way of the two similar flexible braid conductors 28 with the respective half-arms 29a and 29b of the movable member. Said half-arms 29a and 2% are here formed as separate elements, and have their base ends received in an opening formed in an insulating support 36, pivotally mounted in frame 20 by means of pivots 4G. Said support 30 has a semi-cylindrical rib 31 projecting inwardly from a side wall of said opening therein, and the half-arms 29a and 291) have complementary semi-cylindrical recesses 32 which engage with said rib 31 so as to be pivotally movable about the center of said rib as an ideal axis of rotation. Compression springs 33 seated against adjusting screws 34 threaded in support 30 serve to bias the halfarms 29a and 29b separately about this axis towards the stationary pole member 24. Pins 36 extending laterally through the respective half-arms 29a, 29b of the movable member have their outer ends engaging suitable recesses 37 formed in the walls of the support 30 on opposite sides of the opening therein. The pins 36 serve to position the half-arms 29a, 29b in relation to each other and limit the rotational displacements thereof.

To facilitate assembly, the support 30 is in two parts, interassembled with screws such as 39, and is externally formed with the aligned cylindrical cavities 49 coaxial with the semicylindrical rib 31 for receiving the pivots 40' referred to above as serving to mount support 30 for rotation relative to frame 20. It will be noted that a wear-resistant metallic coating 37 is provided over the surfaces of the semi-cylindrical rib 31 and the wall surface of the aperture in support 30 against which the arms 29a, 2912 are biassed by the springs 33.

It will be understood that the support 30 is adapted to be rotated about its pivots 40' relative to frame 20 by suitable means, not shown, such as an electromagnet, between a circuit-making position shown in FIG. 3 in which the movable contact :member 29a-29b engages the stationary contact member 24 as shown in full lines, and a circuit-breaking position in which the movable cont-act member assumes the position shown in phantom in which it is out of engagement with the stationary member. In the circuit-making position shown, the springs 33 press the half-arms 29a and 29b of the movable member separately into engagement with the stationary contact member, whereby the contact pressures in both halves of the assembly can be accurately equalized. In the circuitbreaking position, with support 30 rotated in the counterclockwise direction from the position shown in FIG. 3, the movable contact half-arms 29a and 2915 are pressed by their respective springs 33 into engagement with the wear-taking coating 37 of the support member 30.

As said above, the stationary contact member 24 is largely similar in construction to either of the contact members C in the first embodiment, except that as shown in FIG. 3 said member 24 has no root and base portions corresponding to portions 3a and 1 in FIG. 1, but is instead provided with a base flange which is secured to the conductive frame member 23 by 'means of a screw.

In the :movable contact member 2911-2911, the two sections 29a and 2% together define a general configuration which is basically similar to that of the contact pole members earlier described herein. Thus, as shown in FIG. 4, the half-arms 29a and 2912 are formed with cutouts in their sides facing towards each other so as to define a triangular enlargement 44a of the slot 44 separating said half-arms. The constricted cross section of each half-arm near the base of this triangular enlargement,

7 in the region indicated by the lines S1 and S2 in FIG. 4 and FIG. 3 respectively, is the smallest cross section over the length of the arm, thereby concentrating the current flow lines and imparting a definite direction of fiow thereto as earlier explained.

Further, the geometrical relationships illustrated are such that the mean path of current flow M (FIG. 4) is more remote from the midplane of symmetry passing through the center of slot 44 than is the outer edge 45a of the contact segment 45. As a consequence said mean current path M is caused to curve inwards and upwards in a manner generally similar to what is shown in FIG. 2, thereby again generating a resultant electromagnetic force which will propel the arc inwards (toward slot 44) and upwards (toward quenching tip 47) regardless of the point of initiation of the arc. Also, the arm portions 46 which underlie the contact segments 44 are flat and straight to provide opposite straight parallel spaced segments of substantial length for the current flow paths therethrough, thereby to increase the intensity of the electromagnetic force as described with reference to FIG. 1.

FIGS. 5-7 illustrate a further modified construction for a movable contact member in a circuit breaker according to the invention. The contact member has a body 50 produced from heavy-gauge copper sheet suitably stamped and press-shaped. The stamping includes a median slot 54 which extends from the upper end of the member and terminates in a circular enlargement 55 near the midsection of the member. Silver contact segments 51 are brazed to the copper member on opposite sides of the slot. In cross section the member is U-shaped as shown in FIG. 7 with side flanges 64 extending throughout its length. The member further includes a jutting arcquenching tip or horn 56 at its upper end, a semi-cylindrical rib or knee 52 below the circular cutout 55 for pivoting the member to a support in a manner generally similar to that described with reference to FIGS. 3 and 4, and formations generally designated 53 at the lower end of the member for attachment purposes, which need not here be described in detail. It will be noted that in this embodiment the two half-arms of the contact member are interconnected at their upper ends by a bridging part 56 for greater rigidity of the member as a whole. Preferably, the bridge portion 56 is provided as a separate element made of a high-resistivity metal to minimize the flow of current through the shunt circuit branch thus provided. Such a shunt current if present would tend to repel the arc in a downward direction.

As shown in phantom in FIGS. 6 and 7, the contact member just described cooperates with a stationary contact member which is of similar configuration at least insofar as the upper part of the member is concerned, and includes the two half-arms 60 carrying the contact segments 61 cooperating with segments 51, said halfarms being separated by a median slot 62. This slot terminates at its lower end in an e.g. circular enlargement (not shown) similar to the circular enlargement 55.

Owing to the circular enlargement 55 terminating the slot in each contact member at the lower end of said slot, a constricted current flow section S is defined. In the present embodiment this constriction is L-shaped since the side flanges 64 extend downward beyond the enlargement 55.

As in the preceding embodiments, the geometry of the member is to determined that the mean line of current flow M in this resricted flow section S is more remote from the midplane of symmetry of slot 54 than is the outer edge 51a of the contact segment 51. Consequently the :mean current fiowpath M will be forced to curve inwards towards the outer-lower corner of the related contact segment 51, and will owing to this curvature create a resultant electromagnetic force acting on the arc to drive the arc inwards and upwards as is required and as earlier explained.

More specifically, to ensure that the mean current path M is more distant from the midplane of symmetry than is the outer edge 51a of the contact member, the following geometric relationships are provided in the present construction. As shown in FIG. 7, the width of contact segment 51 is made smaller than the width of the related half-arm of the contact member by an amount somewhat greater than the width of the flange 64, this latter width dimension being equal to the gauge thickness e of the copper stamping; this ensures that the outer edge 51a of the contact segment is substantially closer to the aforemenioned midplane of symmetry than is the midplane of the flange 64. Furthermore, due to the presence of circular enlargement 55, the horizontal leg of the L-shaped cross section C is made shorter than the vertical leg thereof (as viewed in FIG. 7); this in turn ensures that the mean path of current flow M, which must pass substantially through the midpoint of the center line In of cross section S, is located in the vertical leg (as viewed in FIG. 7). Thus the two geometrical features just mentioned combine to ensure that the mean current flow line M is located a greatr distance from the midplane of symmetry of the member than the outer edge 51a of the contact segment is located.

It will be noted from FIGS. 5-7 that the contact segments 51 in this embodiment are provided with bevel surfaces at their upper and lower ends (see FIG. 6) as in the embodiments earlier described, but are not formed with bevel surfaces at their outer edges such as 51a (see FIG. 7). Instead, the flanges 64 of the channel-shaped member are rounded along their outer surfaces where they merge with the inner face of the contact member carrying the contact segments 51. Those rounded surfaces are equivalent in effect to the outer bevel surfaces provided in the other embodiments here disclosed, in imparting an inwardly curved shape to the mean current flow path M as seen on all planes of projection.

Additionally, it will be noted from FIG. 7 that the contact segments 61 of the stationary contact member 60 are somewhat broader than are the contact segments 51 of the movable contact member 50 and extend laterally beyond both opposite side edges thereof, while the median slot 62 of the stationary member is narrower than the slot 54 in the movable member. This relationship is advantageous in that it ensures that the full surface area of the contact segments 51 will always engage the segments 61 irrespective of any lateral displacements between the stationary and operating contact members as may occur due to initial misalignment and due to wear in the moving parts after prolonged service. This averts non-symmetrical wear as between the opposite edges of the contact segments and extends the useful life of the device.

It will be apparent from the foregoing disclosure that the invention has provided an improved form of high-load circuit breaking device in which the geometry of the paths of current conduction is so predetermined that the electromagnetic forces created by the inherent operation of the device during a circuit-breaking action are of such character that they will positively drive an are present across the contact surfaces of the circuit-breaker inward and upward toward arc-quenching means associated with the circuit-breaker. This result is achieved regardless of the precise point over the area of the contact surfaces at which the arc may initiate.

As a consequence the complicated auxiliary means, such as pneumatic or magnetic driving means, conventionally used to propel the arc toward the quenching zone in highcapacity circuit-breakers of the prior art, can be entirely dispensed with.

An essential feature of the geometry of the contact members in a circuit breaker according to the invention, which is responsible for the above result, is the generally inward curvature of the mean line of current conduction leading from the terminal connection at the lower end of the member, to the outer-lower corner of the related contact surface. Such an inwardly curved conduction path was generally absent from prior-art circuit breakers, resulting in the creation of electromagnetic forces which tended to drive the arc in directions other than the inwardupward direction, and consequently necessitating the provision of the afore-mentioned auxiliary arc-propelling means.

In the preferred embodiments of the invention herein disclosed, the inward-curved configuration of the mean path of current flow is obtained primarily through the provision of the enlargement in the median slot of each contact member in the portion thereof between the lower end of the member and the contact surface, and the come quent constricted section of the arm, located generally farther away from the slot than the outermost edge of the contact surface is located. It is to be understood however that many departures from the disclosed constructions may be resorted to while still preserving the basic geometry of the invention.

What I claim is:

1. A high-load circuit breaking device comprising a pair of relatively movable contact members including a stationary contact member and a movable contact member having fiat portions in substantially parallel relationship to each other when in a closed position, bothv in the form of generally channel-shaped arms having channel flanges directed away from each other,

each of said contact members including a protruding contact segment carried on said contact member having a contact surface interengageable with the contact surface on the contact segment on the other of said pair of contact memlbers,

a longitudinal median slot dividing said cont-act member into two half-arms and dividing said contact segment into two half-segments;

means connecting one end of the half-arms of one of said pair of contact members with one terminal of an electric circuit to be broken on relative movement of said contact members to a circuit-breaking position;

means connecting one end of the half-arms of the other of said pair of contact members with another terminal of the electric circuit;

said longitudinal median slot of each of said contact I members having a configuration with an enlargement between said contact segment and the terminal connected ends of said contact members substantially symmetrical with the midplane of symmetry of said contact members and curving generally outward to said terminal connected ends to define a constricted section in each of said half-arms,

said slot in said movable contact member extending throughout the full length of said member and said half-arms of said movable member mounted for independent pivotal movement with respect to said stationar-y member,

and spring means for separately biasing each of said half-arms of said movable member towards a related half-arm of said stationary member whereby during a circuit-breaking action an electromagnetic force will be created in a direction to drive an are set up across said contact surfaces towards said slot and towards the other end of said half-arms away from said terminal connected ends of said contact members.

2. The device defined in claim 1, wherein each halfarm includes a generally flat portion parallel to said contact surface extending over a substantial length between said constricted section and said contact segment.

3. The device defined in claim 1, wherein the contact segments have bevelled outer surfaces connecting the contact surfaces thereof with the surfaces of said arms.

4. The device defined in claim 1, wherein each said arm is a press-formed stamping.

5. The circuit breaking device of claim 1 further characterized by an arc quenching zone positioned adjacent the ends of said contact members away from said terminal connected ends.

References Cited UNITED STATES PATENTS 967,281 8/1910 White 200-147 2,615,109 10/1952 Favre 200147 3,106,627 10/1963 Lisnay 200144 3,132,225 5/1964 Swinehart 200146 FOREIGN PATENTS 100,792 8/ 1923 Switzerland.

ROBERT S. MACON, Primary Examiner.

US. Cl. X.R. 200147 

